After Mrs. Ethel Rogers becomes the second guest on the island to die, speculation immediately arises as to her cause of death. Emily Brent is convinced that Mrs. Rogers died of a guilty conscience. Apparently, this came about as a result of the voice on the recording accusing Ethel and her husband of causing the death of the woman they used to work for by withholding her medication. This was so they could get their hands on her money.
Blore is equally certain that it was Mr. Rogers who murdered his wife in the hopes of keeping their sordid little secret under wraps. In any case, Blore, like Emily Brent, seems to think that Mrs. Rogers got what was coming to her.
The actual circumstances of Mrs. Rogers's death, however, are a good deal more prosaic, but no less sinister. After listening to the accusation on the recording, Ethel faints. When she comes round, she's given a sip of brandy and taken to bed. In the middle of the night, Mr. Rogers tries to wake up his wife, but it's no use; she's dead. That's when all the speculation starts.
But in actual fact, Mrs. Rogers hasn't died of a guilty conscience at all. Instead, it was because someone slipped some chloral hydrate into her brandy, which, along with the sedative given to her by Dr. Armstrong, caused her death by overdose.
That foul play is responsible for Mrs. Rogers's death appears to be confirmed by the fact that there were nine little soldiers on the table before everyone went to bed, and now there are only eight. (The tenth little soldier vanished after the death of Marston.)
To make things just that little bit eerier, it's become clear that the mysterious deaths that have taken place parallel those of the first two little soldier boys in the poem hung upon each guest's bedroom wall. According to the words of the poem, one little soldier "choked his little self, and then there were nine." That, of course, is precisely what happened to Marston, the first guest to die. The next little solider boy "overslept himself and then there were eight." Mrs. Rogers, who's died as a result of a combination of chloral hydrate and sedatives, is this particular soldier.